Implement interface to print runtime information

[kmaehashi]

Implements interface to print runtime information. Took over #4298.
Requires cupy/cupy#1067.

TODO: add test. (done)

[kmaehashi]

Added tests.

Output examples

When CuPy is unavailable:

>>> import chainer
>>> chainer.print_runtime_info()
Chainer: 4.0.0rc1
NumPy: 1.14.2
CuPy: Not Available

When CuPy is available:

>>> import chainer
>>> chainer.print_runtime_info()
Chainer: 4.0.0rc1
NumPy: 1.14.2
CuPy:
  CuPy Version          : 4.0.0rc1
  CUDA Root             : /usr/local/cuda
  CUDA Build Version    : 9000
  CUDA Driver Version   : 9000
  CUDA Runtime Version  : 9000
  cuDNN Build Version   : 7100
  cuDNN Version         : 7100
  NCCL Build Version    : 2102

[niboshi]

LGTM except one comment.

[niboshi]

flush method may not exist.
It's better to either avoid it or test its existence first.

[kmaehashi]

Are there any known file-like class that does not implement flush?
I thought it was a requirement for file-like.
https://docs.python.org/2/library/stdtypes.html#file-objects

[niboshi]

There's no official specification of file-like objects.
You can define an object with only write method and call it a file-like.

[kmaehashi]

OK, I fixed to first check existence of the flush method.
(It seems other features (CupyMemoryProfileHook, ProgressBar, etc...) also assumes flush.)

[niboshi]

I see. It's better to fix them as well.

[niboshi]

Please add testing.run_module(__name__, __file__).

[kmaehashi]

Thanks, fixed.

[niboshi]

LGTM!